JP4537169B2 - Host device and control method thereof - Google Patents

Description

  The present invention relates to a streaming data transfer technique using a communication interface compliant with USB 2.0 or a standard similar thereto.

In data transmission / reception between different media according to sampling rates based on different system clocks, the transmission side of the stream data is the master and the reception side is the slave, receiving the difference between the master (transmitter) clock and the slave (receiver) clock. The slave (receiver) side calculates based on the packet time stamp to be synchronized. Based on the calculated value, the slave (receiver) clock is synchronized with the master (transmitter) clock, and the buffer on the receiving side is overrun or underrun. There is a data communication system that avoids the problem (for example, see Patent Document 1).
Japanese Patent Laid-Open No. 2003-17962 Universal Serial Bus Specification Revision 2.0, April 27, 2000

  However, in the prior art, only the case where the master is the transmission side and the slave is the reception side is described. In other words, in a transfer system that can be configured such that the opposite master is the receiving side and the slave is the transmitting side, such as USB, no solution is given. Cannot be resolved.

  The present invention is intended to solve the above-described problems, and is capable of synchronizing data processing such as decoding and display of received data, and a data transfer system capable of avoiding buffer overruns and underruns. An object is to provide a data transfer method.

An apparatus according to the present invention is a host apparatus that communicates with a slave apparatus via a predetermined interface and receives data transmitted from the slave apparatus. The host apparatus requests stream data from the slave apparatus. Transmitting means for transmitting a data transfer request, measuring means for measuring an interval of the data transfer request based on the clock of the host device, and the data transfer request measured based on the clock of the slave device from the slave device Data processing request relating to the received stream data based on the receiving means for receiving the interval of the data transfer request, the interval of the data transfer request measured by the measuring means, and the interval of the data transfer request received by the receiving means Control means for executing a synchronization process for this purpose .

  According to the present invention, it is possible to synchronize data processing such as decoding and display of received data in streaming transfer using a USB or similar communication interface in which a master receives and a slave transmits, and buffer overrun, Underrun can be avoided.

  Embodiments of the present invention will be described below with reference to the drawings.

  In the present embodiment, a case where the present invention is applied to a system including a personal computer and a digital video camera will be described. The digital video camera according to this embodiment is a composite apparatus having a function of performing streaming reproduction by transferring an input image from a CCD and an input sound from a microphone to a personal computer.

  FIG. 1 is a block diagram showing a configuration of a system in which a personal computer and a digital video camera according to an embodiment are connected. In FIG. 1, reference numeral 100 denotes a personal computer, which functions as a USB host. Reference numeral 101 denotes a USB cable. A digital video camera (DVC) 102 is a USB device having a USB port. In this system, a personal computer 100 and a video camera 102 are directly connected by a USB cable 101, and a moving image and sound being captured by the video camera 102 are transferred to the personal computer as stream reproduction data.

  In this embodiment, the personal computer 100 is a master (host), and the video camera 102 is a slave. Further, as the data transfer direction, the direction from the video camera 102 (slave) to the personal computer 100 (host) is referred to as Up Stream, and the transfer system in the embodiment has an Up Stream streaming function, which will be described.

  FIG. 2 is a block diagram illustrating a configuration of the digital video camera 102 according to the embodiment. In FIG. 2, reference numeral 200 denotes a lens through which light from a subject passes, and 201 denotes an image sensor (CCD). The light from the lens 200 is imaged on the imaging surface, and an electric signal corresponding to the image formed is output. To do. A camera signal processing unit 202 performs signal processing so that a photoelectric conversion image from the image sensor 201 becomes a standard image signal. An image compression / decompression unit 203 encodes and compresses an image signal using MPEG2 or the like. An audio compression / decompression unit 204 compresses an audio signal generated from the microphone 206 by, for example, AC3 encoding and performs audio processing. A multiplexing processing unit 205 multiplexes the image data and the audio data compressed by the image compression / decompression unit 203 and the audio compression / decompression unit 204 by packetizing them in, for example, the MPEG2-TS (Transfer Stream) format. The microphone 206 is used to acquire sound. An audio signal processing unit 207 performs signal processing so that the audio signal from the microphone 206 becomes a standard audio signal. A CPU 208 controls the operation of the entire digital video camera according to a control program stored in the memory 209. The memory 209 is also used as a memory for temporarily storing image data and audio data. Reference numeral 210 denotes a USB controller. Reference numeral 211 denotes a connector for attaching / detaching the USB cable.

  FIG. 3 is a flowchart for explaining the flow of processing during streaming in the personal computer 100 (host).

  In S1000, a Set_Interface command is thrown to the video camera 102 (slave) to start streaming. In S1001, an In token is issued to the video camera 102 (slave), and at the same time, a time when the In token is issued by the personal computer (host) in S1002 is recorded. In S1003, streaming data is acquired from the video camera 102 (slave).

  In S1004, an In token for the next USB packet is issued, and in S1005, the issue time of S1004 is recorded in the personal computer (host). In S1006, from the In token issuance time stored in S1002 and S1005, the issuance interval between In tokens measured by the clock of the personal computer (host) is calculated. In step S1007, streaming data is received. In step S1008, information on the In token interval measured by the video camera 102 (slave) in the header of the streaming packet data received in step S1007 is acquired.

  In S1009, the In token interval measured with the clock of the personal computer (host) calculated in S1006 is compared with the In token interval measured with the clock of the video camera (slave) received in S1008.

  If the In token interval of the video camera (slave) is narrower than the In token interval of the personal computer (host), up sampling is performed on one or both of the image data and the audio streamed in S1010.

  Conversely, if the In token interval of the video camera (slave) is wider than the In token interval of the personal computer (host), one or both of the data of the image and / or audio streamed in S1011 is down sampled. The steps from S1004 to S1011 are repeated until the streaming is completed.

  FIG. 4 is a flowchart for explaining the flow of processing during streaming in the video camera 102 (slave).

  USB connection is performed in S2000. In S2001, the In token issued from the personal computer (host) is received. In S2002, the time when the In token is received in S2001 is stored in the video camera (slave). In S2003, the streaming data is transmitted to the personal computer (host) in response to the request for the In token received in S2001.

  In S2004, an In token for the next streaming transfer is received. In S2005, the time of the In token received in S2004 is stored in the video camera (slave). In S2006, the In token interval measured by the clock of the video camera (slave) is calculated from the In token time recorded in S2002 and the In token time stored in S2005. In S2007, the In token interval measured by the video camera (slave) clock calculated in S2006 is written in the header of the stream to be transmitted in S2008. In S2008, streaming is transmitted according to the In token requested in S2004. The steps from S2004 to S2008 are repeated until the streaming is completed.

  FIG. 5 explains the timing relationship of data transfer to the personal computer (host) in the video camera (slave).

  In this embodiment, a digital video camera has been described as an example. However, the present invention is not limited to this, and any electronic device that can be connected by a USB or a similar interface may be used.

  In this embodiment, data transfer by USB between the digital video camera and the personal computer has been described. However, any data transfer method using USB or a similar interface may be used.

  As described above, according to the present embodiment, in streaming transfer using a USB or similar communication interface that is received by the master and transmitted by the slave, the slave simply stores data and subtracts the stored data. The data necessary for synchronization between transmission and reception can be configured with a simple configuration, and in the host, simple data such as data storage and subtraction between stored data and synchronization data received from the slave can be used. Up / down sampling can be performed, and buffer overrun and underrun can be avoided by synchronizing decoding and display of received data.

It is the image figure which connected the digital video camera and the personal computer. It is a block diagram which shows the structure of a digital video camera. It is a flowchart explaining operation | movement of a personal computer (host). 5 is a flowchart for explaining the operation of the digital video camera. This explains the timing relationship of data transfer to a personal computer (host) in a video camera (slave).

Explanation of symbols

100 USB host (PC)
101 USB cable 102 USB device (digital video camera)
200 Lens 201 CCD
202 Camera Signal Processing Unit 203 Image Compression / Expansion Unit 204 Audio Compression / Expansion Unit 205 Multiplexing Processing Unit 206 Microphone 207 Audio Signal Processing Unit 208 CPU
209 Memory 210 USB controller 211 USB connector

Claims (7)

A host device that communicates with a slave device via a predetermined interface and receives data transmitted from the slave device,
Transmitting means for transmitting a data transfer request for requesting stream data to the slave device;
Measuring means for measuring an interval between the data transfer requests based on a clock of the host device;
Receiving means for receiving an interval of the data transfer request measured based on the clock of the slave device from the slave device;
Control means for executing synchronization processing for data processing relating to the received stream data based on the interval of the data transfer request measured by the measuring means and the interval of the data transfer request received by the receiving means A host device . The control means performs up-sampling processing of the stream data when the interval of data transfer requests measured by the measuring means is larger than the interval of data transfer requests received by the receiving means. Item 2. The host device according to Item 1 . The control means performs downsampling processing of the stream data when the interval of data transfer requests measured by the measuring means is smaller than the interval of data transfer requests received by the receiving means. Item 3. The host device according to Item 1 or 2 . The host device according to claim 1, wherein the data processing includes at least one of decoding and display processing of the stream data . 5. The host device according to claim 1, wherein the interval of the data transfer requests measured based on the clock of the slave device is included in stream data transmitted from the slave device. 6. . The host device according to claim 1, wherein the predetermined interface is a USB . A control method of a host device that communicates with a slave device via a predetermined interface and receives data transmitted from the slave device,
A transmission step of transmitting a data transfer request for requesting stream data to the slave device;
A measurement step of measuring an interval between the data transfer requests based on a clock of the host device;
Receiving from the slave device an interval of the data transfer request measured based on the clock of the slave device;
A control step of executing a synchronization process for data processing related to the received stream data based on the interval of the data transfer request measured in the measurement step and the interval of the data transfer request received by the receiving step A method for controlling a host device comprising:

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